What is it?

There is some disagreement in the tech world about what counts as "wireless charging". Current smartphones and other gadgets that can be powered without plugging in require users to place them on a magnetic surface, a technology commonly known as "inductive" or "near-field" charging.

Some have claimed that this does not count as truly wireless. Firstly, it still requires physical contact, and secondly, at some point in the future we are likely to have far-field wireless charging, in which power is beamed over the air in the same way that Wi-Fi is today.

Wireless charging

It should be noted that Apple refers to the Apple Watch, which is charged by placing it on a pad, as using "magnetic charging", and it may do the same in the iPhone 8. Other companies such as Samsung are happy to call it wireless charging.

How does it work?

Wireless charging pads work by creating an electromagnetic field that allows a current to flow between the surface and the phone placed on it.

Power from the mains creates a current at a transmitting coil in the charger. Phones that use wireless charging feature their own receiver coil attached to the battery that picks up the magnetic field.

Alternatively, phones can use an adapter or case that features the receiver coil and plugs into the phone's charging port.

Nikola Tesla is credited with early work on wireless charging

The concept has been around for more than a century, and early work is widely credited to Nikola Tesla, but it is only in recent years that it has caught on.

The drive has largely been led by gadget manufacturers and often requires users to buy a separate mat. Optimists hope that in future restaurants, hotels and offices will be kitted out with wireless charging pads on desks and tables that will work with any device.

What about the iPhone 8?

One or more of the new iPhones that Apple is expected to unveil today will probably feature wireless charging. The high-end iPhone 8 model is widely believed to include the technology, but the so-called 7s and 7s Plus models could also include it.

While Apple is notoriously secretive, a few hints and details from respected sources have leaked out about how it will work.

What will the iPhone 8 look like?

Apple recently joined the Wireless Power Consortium, whose members also include Samsung, LG, HTC and Huawei, suggesting it will use the most popular standard known as Qi charging. The rival AirFuel Alliance supports a different technology.

Recent reports suggest that Apple may require licences to be compatible with the new iPhone's wireless charging, so existing products may not work. Apple is also expected to have its own wireless charging pad, which may not be on sale until weeks after the new iPhone is launched.

I’ve heard that inductive charging will (a) be sold separately, and (b) might be late, waiting for iOS 11.1 (a la Portrait mode last year). https://t.co/N65dHMNQIJ

How fast is wireless charging?

Wireless charging can be slower and more expensive than the more traditional plug-in method, since the way energy is transferred is less efficient than simply plugging in a wire.

As the technology is developed manufacturers are working to make it faster and more efficient. A more advanced "magnetic resonant" charging format allows multiple devices to be placed on a pad and speeds up the charging, although this is yet to make it into phones.

Rumours have suggested the wireless charging on the iPhone 8 could be slower than others. Rather than charging at the industry standard 15 watts, it could only support 7.5 watts.

What will the iPhone 8 look like?

What devices be charged wirelessly?

As wireless charging becomes more common it is being used to power everything from smart watches and electric toothbrushes to tablets and cars.

The smartphones that currently support wireless charging include Samsung Galaxy devices from the S6 and Note 5 to date. The Moto Z and Blackberry Priv also feature the technology.

Other devices, such as the iPhone 7 and iPhone 6S, can be charged wireless with an adapter and charging pad.

Where can you power up?

Restaurants and hotels are gradually introducing wireless charging mats. Even if phones do not feature the technology the locations often provide adapters.